(1) A public officer shall, except as otherwise provided in this Constitution, retire from the public service on attaining the age of sixty years.

(2) A public officer may, except as otherwise provided in this Constitution, retire from the public service at any time after attaining the age of forty-five years.

(3) The pension payable to any person shall be exempt from tax.

(4) Notwithstanding clause (1) of this article, a public officer who has retired from the public service after, attaining the age of sixty years may, where the exigencies of the service require, be engaged for a limited period of not more than two years at a time but not exceeding five years in all and upon such other terms and conditions as the appointing authority shall determine.